Solid oxide fuel cell system

ABSTRACT

The present invention provides a solid oxide fuel cell system, which comprises a central support means, a fixture means, a current collection means, a manifold, and at least one fuel cell means, wherein the fuel cell means and the current collection means are moveable in the direction parallel to the axis of the fuel cell means.

FIELD OF THE INVENTION

The present invention relates to novel fuel cell systems. Moreparticularly, the invention relates to solid oxide fuel cell systems.

BACKGROUND OF THE INVENTION

A fuel cell is an electrical device which converts the energy potentialof fuel to electricity through an electrochemical reaction. In general,a fuel cell comprises a pair of electrodes separated by an electrolyte.The electrolyte only allows the passage of certain types of ions. Theselective passage of ions across the electrolyte results in a potentialbeing generated between the two electrodes. This potential can beharnessed to do useful work, such as powering a motor vehicle or homeelectronics. This direct conversion process increases the efficiency ofpower generation by removing mechanical steps required by traditionalpower generating device, such as turbine plants. Additionally, thecombination of higher efficiency and electrochemical processes resultsin an environment-friendly product.

A solid oxide fuel cell (“SOFC”) is a device that is approximately 40%efficient in converting the energy potential of fuel to electricitythrough an electrochemical reaction. SOFC possesses three basic parts:an anode that produces electrons, a cathode that consumes electrons, andan electrolyte that conducts ions but prevents electrons from passing.Unlike many fuel cells, the SOFC is capable of running on multiple typesof fuel (e.g., hydrogen, propane, and diesel) without a separatechemical reformer. Therefore, the SOFC system generates a larger amountof electricity per pound than competitive fuel cell systems, such assystems incorporating proton exchange membrane fuel cells.

There are two general structural types of SOFC, tubular cells and planarcells, in referring to the shape of their respective fuel cells whichare shaped cylinders as or plates. Solid oxide fuel cells operate atrelatively high temperatures, around 850-1000 degrees Centigrade. As aresult of these high operating temperatures, the planar cells sufferfrom difficulties with sealing around the ceramic parts of the cell.Thus, there exists a need for an improved fuel cell system thatgenerates low internal thermal stresses and accordingly has reducedsealing requirements.

SUMMARY OF THE INVENTION

The present invention provides a solid oxide fuel cell system, whichcomprises a central support means, a fixture means, a current collectionmeans, and at least one fuel cell means, wherein the fuel cell means andthe current collection means are moveable in the direction parallel tothe axis of the fuel cell means.

In one aspect, the fuel cell means, e.g. fuel cell tubes, attachesrigidly to the current collection means, such as through a conductivematerial (e.g. conductive paste), and form an assembly that is removableas a single unit. In one embodiment, the fuel cell means mounts onfeatures extending from the surface of the fixture means, e.g. injectorpins (7), in a manner such that the gap between the fuel cell means andthe features extending from the surface of the fixture means issufficiently small to allow operation without a seal between the fuelcell means and the fixture means. In another embodiment, the fuel cellmeans is inserted into a cavity in the fixture means. The length of theelectrolyte and cathode are circumferentially variable so as to createthe exposure of anode for the purpose of facilitating currentcollection. The central support means of the fuel cell system may alsofunction as a fuel reformer.

The fuel cell system may further comprise a manifold, such as ahemispherical dome shape manifold, a heat exchanging means, or anafterburner. The heat exchanging means may be bound or joined by somemechanical means to the central support means. The heat exchanging meansand the central support means may also be manufactured or assembled as asingle unit.

The present invention also provides a solid oxide fuel cell systemcomprising a central support tube, a fuel cell plate, a currentcollection plate, a manifold, and at least one fuel cell tube, whereinthe at least one fuel cell tube and the current collection plates arefree to move in the direction parallel to the axis of the fuel celltubes.

The present invention further teaches a method of converting a fuel intoelectrical energy, comprising the step of introducing the fuel and othermaterials (e.g. air) into a solid oxide fuel cell system, wherein thesolid oxide fuel cell system comprising a central support means, afixture means, a current collection means, and at least one fuel cellmeans, wherein the at least one fuel cell means and the currentcollection means are free to move in the direction parallel to the axisof the fuel cell means.

Additional aspects of the present invention will be apparent in view ofthe description that follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a representative fuel cell system. A central support tube(2) is inserted into a fuel cell stack (1) comprising of multiple fuelcells (3), a fuel cell plate (4), a current collection plate (5), and amanifold (6). The fuel cell plate (4) is affixed to the central supporttube (2) by physical, mechanical, and/or chemical means, such asfriction.

FIG. 2 shows a fuel cell plate with injector pins. The fuel cells (3)are inserted over injector pins (7) which are a feature of the fuel cellplate (4).

FIG. 3 illustrates a fuel cell system with the fuel cells and thecurrent collection plate assembly removed. The assembly of the currentcollection plate (5) and the fuel cells (3) can be removed by slidingthem off the central support tube (2).

FIG. 4 depicts a fuel cell system with central support tube removed.

FIG. 5 shows an alternative fuel cell plate design. The fuel cell plate(4) is formed from an insulating material and the fuel cells (3) areinserted into cavities (8) in the fuel cell plate (4).

FIG. 6 illustrates a fuel cell system with an insulating plate adjacentto the fuel cell plate. A insulator plate (10), which is made ofinsulating material and located adjacent to the fuel cell plate (4) asshown in FIG. 6, is fabricated with openings equal to or slightlysmaller than the fuel cells (3) to reduce gas leakage from fuel cells(3) at the joint with the fuel cell plate (4).

FIG. 7 depicts a side view of one embodiment of a fuel cell. In thisembodiment, a fuel cell (3) comprises an anode (11), a cathode (12), andan electrolyte, wherein the anode (11) is partially exposed in asemi-circular pattern (26).

FIG. 8 is an end view of the fuel cell (3) of FIG. 7.

FIG. 9 shows a current collection plate with a current collection groovepattern (13).

FIG. 10 illustrates the assembly of the current collection plate andfour fuel cell tubes. The current collection groove pattern (13) may befilled with a conductive paste (14) following the insertion of the fuelcells (3).

FIG. 11 depicts a fuel cell system with a heat exchanger at the end ofthe central support tube. The heat exchanger (9) preheats the fuel airmixture prior to entering the central support tube (2) using the heatextracted from the stack (1) exhaust gas.

FIG. 12 shows a fuel cell system with the heat exchanger and the centralSupport tube assembly removed. The heat exchanger (9) may be bound orotherwise attached to the central support tube (2) or manufactured as anintegral part of the central support tube (2). As shown in FIG. 12, theheat exchanger (9) and the central support tube (2) may be removed as anassembly from the stack (1) to facilitate maintenance or replacement.

FIG. 13 illustrates a fuel cell system with a dome-shaped manifold. Themanifold at the end of the stack is subject to thermal stresses duringfuel cell operation. A dome-shaped manifold (15) reduces the thermalstresses on the manifold.

FIG. 14 shows a cylindrical and domed of manifold designs. A cylindricalmanifold (6) as shown in FIG. 14 with a planar closure surface (16)experiences thermal expansion dulling the operation of a fuel cell,causing a stress at the intersection of the closure surface (16) and thecylindrical surrounding wall (17). A fillet (18) at the intersection ofthe closure surface (16) and the cylindrical surrounding wall (17)reduces the thermal-induced stresses.

FIG. 15 illustrates a section view of a fuel cell system employing thestack insulation as the gas manifold. The fuel cell assembly is insertedinto an insulation component (19) such that a void space (21) betweenthe fuel cell plate (4) and the insulation component (19) is formed. Thevoid space (21) serves as a gas manifold to provide a path for gases topass from the central support tube (2) to the fuel cells (3).

FIG. 16 depicts a section view of a fuel cell system. A central supporttube (2) is inserted into a fuel cell stack (1) comprising of multiplefuel cells (3), a fuel cell plate (4), a current collection plate (5),and a manifold (6). An afterburner (20) is affixed to the centralsupport tube (2) and combusts unconsumed fuel passing through the stack(1).

FIG. 17 illustrates a section view of a fuel cell system with aninsulation component. The assembly is inserted into the insulationcomponent (19) to prevent the heat associated with the operation of thefuel cells from leaving the assembly.

FIG. 18 shows a section view of a fuel cell system employing the stackinsulation as the gas manifold. The assembly is inserted into aninsulation component (19) such that a void space (21) between the fuelcell plate (4) and the insulation component (19) is formed. The voidspace (21) serves to provide a path for gases to pass from the centralsupport tube (2) to the fuel cells (3).

FIG. 19 depicts a fuel cell (3) with a cathode current collection system(22) that consists of non-insulated wire tightly wrapped around thecathode (12) of the fuel cell. The anode (11) of the fuel cell near theend of the cell is exposed to allow current collection after the fuelcell is inserted into the current collection plate.

FIG. 20 illustrates a fuel cell system with wire wound currentcollection. The cathode current collection (22) is provided by a wirewound tightly around the fuel cells (3) and then threaded through a holein the current collection plate (5). The wires are then wound around theexposed anode material at the end of adjacent fuel cells (3) to form theanode current collection (23). By connecting the anode and cathodes ofadjacent fuel cells (3), the fuel cells (3) are wired electrically inseries. The electrical power generated by the fuel cell is carried outof the system by the power leads (24) and (25) connected to the cathodeand anode of the system respectively.

FIG. 21 displays a current collection scheme which employs conductiveclips (27) to interconnect fuel cells (3) when the fuel cells (3) andconductive clips (27) are inserted into the current collection plate(5). To accommodate the requirement for one end of the conductive clipto contact the anode (11) and the opposite end of the conductive clip(27) to contact the cathode (12) for the adjacent fuel cells (3), ananode clip groove (29) and a cathode clip groove (28) are providedadjacent to the holes in the current collection plate (5) in which thefuel cells (3) mount. A portion of the anode (11) is not covered by theelectrolyte and cathode (12) to facilitate contact with the conductiveclip (27).

FIG. 22 shows the interconnection of the cathode of one fuel cell (3)with anode of the adjacent fuel cell (3) which are inserted in thecurrent collection plate (5) and a conductive clip (27).

FIG. 23 depicts the complete assembly of a current collection systemwith the installation of four fuel cells (3) in the current collectionplate (5) and the connective clips (27). An anode power clip (30) andcathode power clip (31) are installed in the respective anode clipgroove and cathode clip groove. Ceramic filler (32) is installed in thecathode clip groove to prevent the connective clips (27) and the cathodepower clip (31) from moving which could lead to an open circuit or ashort circuit.

DETAILED DESCRIPTION OF THE INVENTION

As used herein and in the appended claims, the singular forms “a,” “an,”and “the” include plural references unless the content clearly dictatesotherwise. Thus, for example, reference to “a combustion catalyst”includes a plurality of such combustion catalysts, and reference to “thefuel cell tube” is a reference to one or more fuel cell tube andequivalents thereof known to those skilled in the art, and so forth. Allpublications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety.

The present invention provides a fuel cell system, which comprises acentral support tube, a fuel cell plate, a current collection plate, aplurality of fuel cell tubes, and optionally, a manifold, an insulationmeans, a heat exchanger, or an afterburner. In one embodiment, thedesign of the fuel cell system allows unrestricted expansion andcontraction of the fuel cell tubes during the thermal cycles associatedwith starting and stopping the system, thereby reducing or eliminatingthermal stresses that can cause premature failure of solid oxide fuelcells. In addition, the fuel cell system is designed in such a mannerthat the fuel cell tubes as well as a fuel reformer and a heat exchangercan be easily removed for maintenance or replacement.

The central support tube (2), the fuel cell plate (4), and the currentcollection plate (5) may be made of any materials suitable for SOFCsystem, e.g. ceramic materials. The central support tube (2) may beconnected with the fuel cell plate (4) through a number of mechanisms,such as by friction or by mechanical interactions. FIG. 1 discloses atubular solid oxide fuel cell system design, wherein the central supporttube (2) is attached to the fuel cell plate (4) by merely friction. Thejoint between the central support tube (2) and the fuel cell plate (4)may be a tight slip fit such that friction holds the fuel cell plate (4)in place on the central reformer tube.

The central support tube (2) may also function as an integral reformerto convert fuel (e.g. propane) to carbon monoxide and hydrogen suitablefor reaction by the solid oxide fuel cells. In a preferred embodiment,the reformer is a partial oxidation reformer. For example, when propaneis used as fuel, the partial oxidation reformer converts it into CO andH₂:C₃H₈+1.5 O₂→3 CO+4 H₂

In one embodiment, the fuel cells (3) mount on features of the fuel cellplate (4) called injector pins (7) as shown in FIG. 2. The injector pins(7) may be formed as integral features of the fuel cell plate (4) ormanufactured separately and assembled to the fuel cell plate (4). Thediameter of the fuel cell tubes (3) may be slightly bigger than that ofthe injector pins (7) such that a narrow gap is formed when a fuel celltube (3) is mounted on an injector pin (7). No separate seal is neededto prevent reformate (gaseous fuel) leakage because the pressure dropsthrough the narrow gap between the injector pin (7) and the inside ofthe fuel cell (3) is much higher than the pressure drops through thefuel cell chamber and thus there is sufficient back pressure to minimizethe leakage of reformate (gaseous fuel) from the inside of the fuel celltubes (3) without the use of a separate seal. For example, a fuel cell(3) with a 2.8 mm diameter may be mounted to an injector pin (7) with a2.5-2.7 mm diameter and the gap thus formed does not interfere with theoperation of the fuel cell system. In another embodiment, the fuel cells(3) are mounted onto the fuel cell plate by inserting them into cavities(8) in the fuel cell plate (4), as shown in FIG. 5. The diameter of thecavities (8) may equal or be slightly smaller than that of the fuel celltubes (3).

To increase further the pressure drops through the narrow gap, aninsulation means, such as a plate (10) made of insulation material, maybe installed in proximity to the fuel cell plate (4), as shown in FIG.6. The term “in proximity” as used herein refers to a state whereinthere is no gap between the adjacent components or even if there is agap between two adjacent components, the gap is sufficiently small so asnot to interfere with the function of the components, which, in thepresent case, is to create back pressure to minimize gas leakage. Theinsulation plate (10) may comprise a combustion catalyst which, in casesof fuel leakage, converts the leaked fuel to CO₂, and therefore, helpsmaintaining the non-reducing environment outside the channels of thefuel cell tubes (3).

Similarly, the narrow gap between the central support tube (2) and thefuel cell plate (4) and optionally, the insulation plate (10), preventsleakage of reformate through the gap between these two componentswithout using a separate seal.

The fuel cells (3) are connected to the current collection plate (5) asshown in FIG. 1. In one embodiment, each cell is electrically connectedto the current collection plate (5) by a current collection system whichinterconnects the fuel cells (3) with the appropriate combinations ofparallel and series connections to produce the desired output voltage. Anumber of mechanisms may be employed to facilitate current collection.In one embodiment, the fuel cell tube (3) is fabricated in such a mannerthat the cathode and anode are exposed in a specific pattern, as shownin FIGS. 7-10 and 21-23, such that when the fuel cell (3) is insertedinto the current collection plate (5) in the proper orientation, thepattern is appropriately positioned to allow the application of aconductive paste or clip to interconnect the anodes and cathodes ofadjacent fuel cells (3) as desired. For example, a pattern ofdepressions may be incorporated into the fuel cell plate (4), as shownin FIG. 9, to facilitate the application of the conductive paste tointerconnect the fuel cells (3) as shown in FIG. 10. The fuel cells (3)may be fabricated to include features such a local flats, protrusions,or grooves which align with corresponding features in the currentcollection plate (5) to insure the proper orientation of the fuel cellcathode and anode patterns with the current collection plate (5).Alternatively, a fuel cell (3) may be manufactured such that the anode(11) is partially exposed in a semi-circular pattern (26), as shown inFIGS. 7-8. Conductive clips (27) are used to interconnect fuel cells (3)when the fuel cells (3) and the conductive clips (27) are inserted intothe current collection plate (5), as shown in FIG. 21-23. To accommodatethe requirement for one end of the conductive clip (27) to contact theanode (11) and the opposite end of the conductive clip (27) to contactthe cathode (12) for the adjacent fuel cells (3), an anode clip groove(29) and a cathode clip groove (28) are provided adjacent to the holesin the current collection plate (5) in which the fuel cells (3) mount.Ceramic filler (32) is installed in the cathode clip groove to preventthe connective clips (27) and the cathode power clip (31) from movingwhich could lead to an open circuit or a short circuit (FIG. 23). Thecurrent collection from the fuel cell tubes (3) may be accomplishedthrough the use of wire (e.g. silver wire) or other suitable means tointerconnect the anodes and cathodes of the individual fuel cells (3).FIGS. 19-20 discloses another current collection scheme, wherein thecathode current collection (22) is provided by a wire wound tightlyaround the fuel cells (3) and then threaded through a hole in thecurrent collection plate (5). The anode (11) of the fuel cell (3) nearthe end of the cell is exposed to allow current collection after thefuel cell (3) is inserted into the current collection plate. The wiresare then wound around the exposed anode material at the end of adjacentfuel cells (3) to form the anode current collection (23). By connectingthe anode and cathodes of adjacent fuel cells (3), the fuel cells (3)are wired electrically in series. The electrical power generated by thefuel cell (3) is carried out of the system by the power leads (24) and(25) connected to the cathode (12) and anode (11) of the systemrespectively.

In one embodiment, the current collection plate (5) is a slip fit overthe central support tube (2) and moveable along the direction parallelto the axis of the fuel cell tubes (3). The term “moveable” as usedherein refers to the changing of relative position between the twosubjects, such as the current collection plate (5) and the centralsupport tube (2). It also refers to the changing of relative positionbetween a portion of one subject (e.g. the extending or retracting of aportion of a fuel cell tube (3) such as the anode (11) end of a fuelcell (3)) with another subjects (e.g. the central support tube (2)). Thecombination of the current collection plate (5) and the fuel cells (3)may slide along the central support tube (2). During the operation ofthe fuel cell system, the current collection plate/fuel cell assembly isexpandable longitudinally as a result of the clearance between thecentral support tube (2) and the current collection plate (5). Thisfreedom of movement minimizes longitudinal compressive forces beingapplied to the fuel cells (3).

In one embodiment, the current collection and fuel cell assembly caneasily be removed from the stack for maintenance and replacement sinceit simply slips over the central support tube (2) as shown in FIG. 3. Inanother embodiment, the central support tube (2) can be removed fromstack because it is a tight slip fit (friction fit) into the fuel cellplate (4) as shown in FIG. 4.

An alternative design of the fuel cell plate (4) is shown in FIG. 5wherein the plate, which is normally made of alumina or a similarceramic material, is constructed using an insulation material, forexample, 2-8 micron alumina fiber. In this design, the gap between thecentral support tube (2) and the fuel cell plate (4) can be largerbecause the depth of insertion of the central support tube (2) into thefuel cell plate (4) is greater, resulting in a large pressure dropbetween the inside of the fuel cell tube (3) and the area surroundingthe fuel cell tube (3) and thus minimizing gas leakage.

In one embodiment, an insulator plate (10) is located in proximity tothe fuel cell plate (4) as shown in FIG. 6. The holes through which thefuel cell tubes (3) pass in the insulator plate may be fabricated at adiameter equal to or slightly smaller than the individual fuel celltubes (3) causing a tight fit between the fuel cells (3) and theinsulator plate. The insulator plate (10) may be bound to the fuel cellplate (4) through chemical or physical means, such as alumina bondingagent or friction. The resulting fuel cell plate/insulator plateassembly produces an increased resistance to fuel leakage due to a largepressure drop between the inside of the fuel cell tube (3) and the areasurrounding the fuel cell tube (3).

The central support tube, which may hold a chemical reformer in someapplications, may also be attached to, or comprise, a heat exchanger ora afterburner as shown in FIGS. 10, and 16-18. This heat exchangerextracts heat from the fuel cell stack exhaust gas which it then uses topreheat the intake fuel/air mixture. The afterburner achieves the sameeffect by converting unconsumed fuel to heat using a combustioncatalyst, such as Pt/Al₂O₃ particles, PtRh/CeO₂/AlO₃ pellet, andPt/α-Al₂O₃ foam monolith. The heat exchanger/afterburner and the centralsupport tube (2) assembly can be removed from the stack for maintenanceor replacement as shown in FIG. 11.

The heating of the manifold during the operation of the fuel cells (3)creates thermally induced stresses. Installation of a manifold (15)which is shaped in the form of a hemispherical dome as shown in FIG. 13reduces the stress concentrations within the manifold. As shown in FIG.14, the manifold (6) with a planar closure surface (16) experiencesstress concentration at the intersection of the closure surface (16) andthe cylindrical side walls (17). A fillet (18) at the intersectionreduces the thermal-induced stress. A hemispherical shaped manifold (16)further reduces the stress concentration thereby reducing the weight ofthe manifold. In one embodiment, the function of the manifold may beperformed, as shown in FIG. 18, by binding the current collection plate(5) to an insulation component that is gas impermeable. This eliminatesthe separate manifold part and may reduce the overall cost of thesystem.

EXAMPLE

The following example illustrates the present invention, which is setforth to aid in the understanding of the invention, and should not beconstrued to limit in any way the scope of the invention as defined inthe claims which follow thereafter.

The following example describes the construction of a fuel cell systemwith 36 fuel cells. The current collection plate, the fuel cell plate,and the manifold cap were made of alumina or macor and manufacturedfollowing a gel casting process as known in the art. The central supporttube was constructed from an extrude alumina tube, which was tested byfiring it to 1550° C. A dense Saffil fiber board was used to constructthe insulation plate, whilst a Saffil felt was used for making gaskets.

The fuel cell plate, the current collection plate, the manifold cap, andthe insulation plate were pre-fired to 950° C. to ensure that theseparts were suitable for high temperature applications. Additionalfeatures, such as holes or grooves for thermocouples, currentcollection, or air flow, were added to the parts. Injector pins weremade by cutting a pre-extruded alumina tube (O.D. 2.6 mm; I.D. 1.4 mm).The length of the injector pins was between 5-15 mm depending on thelength of the fuel cell. The injector pins were then assembled and fixedonto the fuel cell plate by using an alumina bonding agent, Resbond 989Hi-Purity Alumina Ceramic, and then cured at 600° C. for 2 hours toensure that an appropriate seal was formed.

36 tubular fuel cells were prepared according to the method disclosed inU.S. patent application Ser. No. 60/526,398 entitled “Anode-SupportedSolid Oxide Fuel Cell Using a Cermet Electrolyte.” The fuel cells werethen assembled into the current collection plate. Electrical connectionswere made to achieve the desired output voltage. For example, a 36 Voutput would require the 36 fuel cells to be wired in series, while an18 V output would require that the 36 fuels be wired in series as 18pairs. The electrical connections between the cells were made by using acombination of conductive metal plate/foam and/or conductive paste, suchas silver and Ni/YSZ cermets. This assembly was then dried at 70° C. for2 hours. A layer of alumina bonding agent was then added to the top ofthe current collection plate to seal the connection between the currentcollection plate and the fuel cells.

The reforming catalyst was added into the central supporting tube. Thefour segments of the catalyst were added sequentially to ensure that thePOX catalysts were fitted first so that the reforming/combustionreaction flows exothermic to endothermic (segments 1 through 4). Thecatalyst segments were secured into position with an alumina-bondingagent (Resbond 989 Hi-Purity Alumina Ceramic). The central supportingtube was then cured at 70° C. for 4-6 hours.

The completed central support tube and the fuel cell plate were bondedtogether using Resbond 989 Hi-Purity Alumina Ceramic. This assembly wasthen cured for 2 hours at 70° C. Two Saffil felt gaskets were placedover the injector pins. The assembly containing the fuel cells and thecurrent collection plate and the assembly containing the central supporttube and the fuel cell plate were assembled together as shown in FIG. 3.

The manifold was attached to the fuel cell plate, and the insulationplate was positioned over the current collection plate. The afterburnercatalyst was placed around the central support tube at a location whichis 10 mm above the insulation plate. Saffil felt was then wrapped aroundthe afterburner catalyst until the OD of the afterburner catalyst andthe Saffil felt was equal to the OD of the current collection plate. Theassembly, or the “stack,” including thermocouples and insulating tubingfor the positive and negative wires, was then cured for 4 hours at 70°C.

The stack was then slid into a tubular heat exchanger which has an IDslightly larger than the OD of the fuel cell plate and the currentcollect plate. The heat exchanger was located such that the holes on theinternal wall of the heat exchanger were in line with the start of theactive electrode on the fuel cell. This assembly was then fitted into asuitable insulation package, which was constructed such that thetemperature of external interface of the fuel cell system is kept below80° C. during the operation of the system.

The fuel cell system was tested under the following conditions. Thesystem was started on an oxygen/propane fuel (2.4:1, respectively) at aflow rate 1-2.5 L/min. Ignition was accomplished using an electronicigniter located at the back of the afterburner. The system reached 700°C. in less than 10 minutes. At this point the oxygen/propane ratio wasaltered to between 1.8 and 2.2 depending on desired load of the system(full load=1.8; low load=2.2). The ratios were varied to maximizehydrogen production during high load demand and to balance the operatingtemperature of the stack, which increased to 850° C. under full load.The system produced 57 W at 835° C. when operated with an oxygen/propaneratio of 1.9. The system was then shut down on a reduced fuel flow rate(¼ of full flow), whilst maintaining an oxygen/propane ratio of 2.2.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be appreciated by oneskilled in the art, from a reading of the disclosure, that variouschanges in form and detail can be made without departing from the truescope of the invention in the appended claims.

1. A solid oxide fuel cell system comprising: a fuel cell plate; acentral support tube associated with the fuel cell plate; a tubular fuelcell associated with the fuel cell plate; a current collection plateelectrically connected to the tubular fuel cell, wherein the currentcollection plate is slidably attached to the central support tube; andan insulator plate between the fuel cell plate and the currentcollection plate, wherein the insulator plate comprises a combustioncatalyst.
 2. The solid oxide fuel cell system of claim 1, wherein thecurrent collection plate is slip fit over the central support tube. 3.The solid oxide fuel cell system of claim 1, wherein the central supporttube is friction fit into the fuel cell plate.
 4. The solid oxide fuelcell system of claim 1, wherein the fuel cell plate comprises aninjector pin.
 5. The solid oxide fuel cell system of claim 4, whereinthe tubular fuel cell is mounted on the injector pin.
 6. The solid oxidefuel cell system of claim 5, wherein the tubular fuel cell is mounted onthe injector pin without a seal.
 7. The solid oxide fuel cell system ofclaim 6, wherein the injector pin is integral to the fuel cell plate. 8.The solid oxide fuel cell system of claim 1, wherein the fuel cell platecomprises a cavity and the tubular fuel cell is inserted into thecavity.
 9. The solid oxide fuel cell system of claim 1, wherein thecentral support tube comprises a fuel reformer.
 10. The solid oxide fuelcell system of claim 1, wherein the central support tube and the tubularfuel cell are in fluid communication via a manifold.
 11. The solid oxidefuel cell system of claim 10, wherein the manifold is dome-shaped. 12.The solid oxide fuel cell system of claim 1, wherein the central supporttube, the current collection plate, the insulator plate, the fuel cellplate, and the tubular fuel cell comprise a fuel cell assembly, and thefuel cell assembly is inserted into an insulation component.
 13. Thesolid oxide fuel cell system of claim 12 comprising a void space betweenthe fuel cell plate and the insulation component.
 14. The solid oxidefuel cell system of claim 13, wherein the void space is adapted tofunction as a manifold.
 15. The solid oxide fuel cell system of claim 1,wherein the tubular fuel cell comprises an electrolyte, a cathode, andan anode, and wherein the electrolyte and the cathode of the tubularfuel cell comprise a length that is circumferentially variable to exposethe anode of the tubular fuel cell.
 16. A solid oxide fuel cell systemcomprising: a fuel cell plate; a central support tube associated withthe fuel cell plate; a tubular fuel cell associated with the fuel cellplate; a current collection plate electrically connected to the tubularfuel cell, wherein the current collection plate is slidably attached tothe central support tube; at least one of a heat exchanger and anafterburner attached to the central support tube; an insulator platebetween the fuel cell plate and the current collection plate; and amanifold in fluid communication with the tubular fuel cell, wherein thefuel cell plate comprises an injector pin, the central support tubetogether with at least one of the heat exchanger and the afterburnerform a single removable assembly, and the tubular fuel cell and thecurrent collection plate form a single removable assembly.
 17. The solidoxide fuel cell system of claim 1, wherein the current collection platecomprises a plurality of depressions and a conductive paste is appliedto the depressions.
 18. The solid oxide fuel cell system of claim 1,wherein a plurality of conductive clips are inserted into the currentcollection plate.